For married couples, finding moments to be together free of financial, family or other stresses is not an indulgence, according to new research from the University of Denver.

“The more you invest in fun and friendship and being there for your partner, the happier the relationship will get over time,” says Howard Markman, a psychologist who co-directs the University’s Center for Marital and Family Studies. “The correlation between fun and marital happiness is high, and significant.”

Other studies, too, have found that having fun together — especially while doing “new and exciting activities” — is the secret to a happy marriage. Having a joyful marriage is unfortunately the exception rather than the rule in the United States. This is tragic as your happiness and ability to be optimally productive in your life is severely limited when you are not in a happy relationship with your spouse.